1. Field of the Invention
Embodiments of the invention generally provide a substrate support utilized in semiconductor processing and a method of fabricating the same.
2. Description of the Background Art
Liquid crystal displays or flat panels are commonly used for active matrix displays such as computer and television monitors, personal digital assistants (PDAs), cell phones and the like. Generally, flat panels comprise two glass plates having a layer of liquid crystal material sandwiched therebetween. At least one of the glass plates includes at least one conductive film disposed thereon that is coupled to a power supply. Power supplied to the conductive film from the power supply changes the orientation of the crystal material, creating a pattern such as text or graphics seen on the display. One fabrication process frequently used to produce flat panels is plasma enhanced chemical vapor deposition (PECVD).
Plasma enhanced chemical vapor deposition is generally employed to deposit thin films on a substrate such as a flat panel or semiconductor wafer. Plasma enhanced chemical vapor deposition is generally accomplished by introducing a precursor gas into a vacuum chamber that contains a substrate. The precursor gas is typically directed through a distribution plate situated near the top of the chamber. The precursor gas in the chamber is energized (e.g., excited) into a plasma by applying RF power to the chamber from one or more RF sources coupled to the chamber. The excited gas reacts to form a layer of material on a surface of the substrate that is positioned on a temperature controlled substrate support. In applications where the substrate receives a layer of low temperature polysilicon, the substrate support may be heated in excess of 400 degrees Celsius. Volatile by-products produced during the reaction are pumped from the chamber through an exhaust system.
Generally, large area substrates utilized for flat panel fabrication are large, often exceeding 550 mm×650 mm, and are envisioned up to and beyond 4 square meters in surface area. Correspondingly, the substrate supports utilized to process large area substrates are proportionately large to accommodate the large surface area of the substrate. The substrate supports for high temperature use typically are casted, encapsulating one or more heating elements and thermocouples in an aluminum body. Due to the size of the substrate support, one or more reinforcing members are generally disposed within the substrate support to improve the substrate support's stiffness and performance at elevated operating temperatures (i.e., in excess of 350 degrees Celsius and approaching 500 degrees Celsius to minimize hydrogen content in some films). The aluminum substrate support is then anodized to provide a protective coating.
Although substrate supports configured in this manner have demonstrated good processing performance, small local variations in film thickness, often manifesting as spots of thinner film thickness, have been observed which may be detrimental to the next generation of devices formed on large area substrates. It is believed that variation is glass thickness and flatness, along with a smooth substrate support surface, typically about 50 micro-inches, creates a local capacitance variation in certain locations across the glass substrate, thereby creating local plasma non-uniformities that results on deposition variation, e.g., spots of thin deposited film thickness.
Aging and modifying plasma conditioning of the substrate support has shown to mitigate thin spot formation, particularly when performed in conjunction with an extended chamber vacuum purge before transferring a substrate into the chamber for processing. However, the resultant expenditures of time and materials required by this method and its unfavorable effect on cost and throughput make obtaining a more effective solution desirable.
As the size of next generation of substrates continues to grow, the importance of defect reduction becomes increasingly important due to the substantial investment by the flat panel manufacturer represented by each substrate. Moreover, with the continual evolution of device critical dimension reduction demanding closer tolerances for film uniformity, the reduction and/or elimination of film thickness variation becomes an important factor for the economic production of the next generation devices formed on large area substrates.
Therefore, there is a need for an improved substrate support.